1. Field of the Invention
This invention relates to a rotate/rotate type X-ray computerized tomograph apparatus or system, and more particularly to an apparatus or system for obtaining the tomograph of an object being examined by a method wherein high-tension voltage is applied to an X-ray tube so that pulses of X-ray are radiated upon an object being examined and the X-rays that have passed through the object are detected by an X-ray detector and the detected signals are processed by a processor, such as a computer, to produce the tomograph.
2. Description of the Prior Art
A conventional X-ray computerized tomograph system heretofore used is shown in FIG. 1. The system comprises an X-ray tube 1, which outputs X-rays corresponding to voltage applied across its cathode and anode electrodes. The X-ray usually has a pulse shaped wave because voltage applied thereto usually is a pulse shaped wave. An X-ray detector 2 is disposed opposite the X-ray tube 1, with an object 12 being examined disposed therebetween. The tube 1 and detector 2 are movable relative to the object 12. For example, the tube and detector may be rotated about the object 12, such as by means of gantry driving motor 4. The drawing is representational in nature, and intends to show the tube 1 and detector 2 rotating about object 12, by means of a rotator 3. Similarly the object 12 may be rotated with the X-ray tube 1 and detectors held stationary.
X-ray detector 2 is provided with a plurality of detector elements set in an array. Each of the detector elements functions to output current corresponding to the strength of an X-ray incident thereupon after passing through object 12. Rotator 3, to which X-ray tube 1 and detector 2, have been attached, is driven or turned by a gantry driving motor 4 (hereinafter referred to as a motor). A rotation angle detector 5 is connected for detecting the rotation angle of rotator 3 and for providing signals to timing control circuit 11. The timing circuit and rotation detector are known devices, such as described, for example, in U.S. Pat. No. 4,048,503. A group of integrators 6, comprising a plurality of integrators, is connected for integrating currents supplied by each of the elements of the X-ray detector 2. Each integrator is connected to and controlled by timing control circuit 11, described hereinafter, in terms of its integral period so that an integrated value can be obtained on a pulse basis from pulse current inputted successively by X-ray detector 2, at predetermined periods. The integrators are connected to a multiplexer 7, which selects the output of each integrator and transmits the output to a next level. AD converter 8 is connected to the multiplexer 7, for converting an analog signal supplied by multiplexer 7, into a digital signal, and connected to data processor 9 which processes the digital output thereof.
The multiplexer 7 and AD conveerter 8 are connected also to timing control circuit 11. Data processor 9, such as a computer, is connected for receiving signals from converter 8 and for transmitting processed signals to image display unit 10. The processor 9 processes the signal data which is based on the intensity of the X-rays that have passed through the object being examined and transmitted via AD converter 8, thereby to obtain a tomograph. Image display unit 10, which may be a cathode ray tube, displays the resulting tomographs. Timing control circuit 11, which is connected at its input to detector 5, and at its output to integrators 6, multiplexer 7, converter 8, grid control circuits 15 and 16, functions to regulate the timing of various components upon receiving signals from rotation angle detector 5 in a manner to be hereinafter explained in greater detail. The supply circuit comprises high tension switching tubes 13 and 14, which may be tetrode type tubes; grid control circuits 15 and 16; a Y-connected three-phase transformer T.sub.1 ; and rectifiers D.sub.1 -D.sub.12, connected to each other in the manner depicted and connected to X-ray tube 1, to supply high-tension voltage thereto.
The circuitry and components of each of the components set forth in FIG. 1 and other figures in the drawing, are known. These are generally available off the shelf commercially. For example, the AD converter is well known, and can be obtained readily on the market and installed with only the description given herein, and operated to perform the functions set forth herein.
Operation of the conventional X-ray computerized tomograph apparatus of FIG. 1, will now be explained with reference to FIG. 3. The three phase transformer T.sub.1 and the rectifiers D.sub.1 -D.sub.12 make available d.c. voltage, with little voltage regulation, and the d.c. voltage obtained, is applied as high tension voltage to X-ray tube 1, through high tension switching tubes 13,14. FIG. 3 is a time chart wherein (l), (m) and (n) illustrate the action of the components shown in FIG. 1. In FIG. 3, waveform (l) is the output of rotation angle detector 5; waveform (m) is the X-ray pulse irradiated from the X-ray tube 1; and waveform (n) is the behavior of integrator 6. Rotator 3 is suitably turned by motor 4 and its rotation angle is detected by rotation angle detector 5 and a pulse signal (l) is outputted by detector 5 to timing control circuit 11 at every predetermined angle (e.g. every 1.degree.).
As shown in FIG. 1, timing control circuit 11, for example, allows grid control circuits 15,16 to operate syncronously with the trailing edges of pulse (l) thereby to apply a high tension pulse to X-ray tube 1, so that the pulse (m) of X-ray tube 1 is irradiated onto the object 12. The irradiated X-ray pulse (m) passes through object 12, being examined, and is detected by X-ray detector 2. The current measured by X-ray detector 2 shows a pulse waveform synchronized with what is shown by waveform (m) in FIG. 3 and integrator 6 integrates the current in each of waveform (n) periods (1), (3) and (5), to convert the quantity of transmitted X-ray into a voltage value.
On the other hand, for correcting for circuit error factors and the like, integrator 6 also carries on integral control action in periods (2) and (4) shown by waveform (n) in FIG. 3. The integral values obtained in the apparatus in these periods (2) and (4) are the ones when X-ray input is zero. This procedure is often termed zero signal correction. By making equal the time intervals for periods (2) and (4) and those of periods (1) (3) and (5) the zero current variation of an integrator and the like will be corrected, if the values obtained in periods (2) and (4), which represent zero current correction factor, are subtracted from the data signal obtained during periods (1), (3) and (5), that is the signals from the X-ray detector representing the signal transmitted through the object. The integrator 6 is reset during the periods between (1) and (2) and (3). As mentioned, the integrator alternatively repeats integration at the time of X-ray irradiation, resets, zero current correction integration, resets, syncronous with the timing of the pulse shaped high tension voltage applied to the X-ray tube, whereby a tomogram is displayed on the image display unit 10 from the data signal tansmitted through AD converter 8 and data processor 9.
However, the conventional X-ray computerized tomograph system, such as depicted in FIG. 1, has the following deficiencies or disadvantages.
The high tension voltage generator employs a three phase transformer to obtain a semi-d.c. output at .+-.60 kV, so that the generator is likely to be complicated in construction, large sized and costly. The only voltage supply, including a transformer, of the computerized tomograph system currently sold on the market, weighs about 1.3 tons, and is therefore not readily movable.
The prior computerized tomograph system is also very expensive because it requires high tension voltage switching tubes and grid control circuits provided with high tension voltage insulating functions.
Also, in the prior system, even under a no-load condition voltage rises, thus requiring the components to have greater dielectric strength which entails large and expensive components. FIG. 4(I) is a diagram indicating the waveform of output voltage in the loaded and unloaded conditions, as applied by rectifiers D.sub.4 -D.sub.12 (of FIG. 1) as high tension voltage generators. FIG. 4(II) shows the waveform of current flowing into X-ray tube 1.
As shown in FIG. 4, the high tension voltage output in the high tension voltage generator (shown in FIG. 1) fluctuates because the load current (which is the cube of the current) changes. Accordingly, when the desired high tension voltage is supplied to the load, the voltage under a no-load condition rises (see FIG. 4.(I)), thus requiring the components of the high tension voltage generator, including the transformer, to have high dielectric strength, and thus making the system large-sized and expensive. For this reason, in the prior art, the X-ray tube voltage has been limited to approximately 120 kV.